1. Field of the Invention
The present invention relates to a harvesting machine comprising:                a carrier frame comprising lateral uprights on which are articulated pivots equipped with wheels,        first hydraulic jacks which are connected to the lateral uprights and to the pivots,        at least one harvesting mechanism which is provided with cutting members,        a suspension device linking the harvesting mechanism to the frame and allowing a vertical displacement of the harvesting mechanism with respect to the frame and        a lightening device of the harvesting mechanism.        
2. Description of the Related Art
In the known harvesting machines of this type, the lightening device is generally constituted by draw-springs arranged between the frame and the suspension device. These springs then exert an upward traction on the suspension device and the harvesting mechanism and thus transfer a part of their weight on the frame. This lightening prevents the harvesting mechanism from resting too heavily on the ground. It can thus easily follow the differences in level of the ground. This reduces the risk of mishandling the plant cover which could result from too strong a pressure of the said mechanism on the ground. The power to be developed for moving the machine during work can also be reduced. Finally, the wear of the parts of the harvesting mechanism which rub on the ground is less rapid.
The draw-springs currently used on harvesting machines are bulky and cumbersome, particularly when the machine has a large working width. On these machines, there is also a risk of cut products jamming between the turns of these springs, which could harm their functioning. Finally, their cost is relatively high.